What is cancer? Medics speak of a malignant tumor, or carcinoma. All cancers begin in cells, the body's basic unit of life. Both animals and human beings are composed of many different cells that form groups; different groups of cells form organs with specific functions. Every cell contains genetic information in its nucleus, which assigns a particular task to the cell. This genetic information is contained in several long strands that consist of sugar, phosphate, and four different bases (adenine, thymine, guanine, cytosine). These bases are lined up in a row to form the so-called DNA strand. Pairs of these strands combine to form chromosomes. So basically, a cell is put together in the same way an entire organism is put together, but on a much smaller scale. The DNA is like a recipe book in which all instructions are written down with great precision. These processes must be executed in an organized manner; otherwise, the result is chaos. How do these defects in DNA occur? Radioactive irradiation and chemicals may damage the DNA. Depending on the tissue, there are different ways in which it can be damaged. Lung cells do not tolerate cigarette smoke, liver cells do not tolerate alcohol, and kidney cells do not tolerate heavy metals. The entire issue is further complicated by the immune system, which—as we have learned—can recognize and also eliminate tumor cells. However, it can also trigger tumor formation through various factors; e.g., chronic inflammatory stimuli. Therefore, the development of a malignant tumor is an evolutionary process that occurs in one’s own body, and it is caused by a deregulated cell. Now it becomes clear as to why substances capable of damaging genetic information can trigger tumor formation. In short, anything that can disorganize the recipe book of a cell can cause tumor formation. This video will help you understand how cancer cells occur in the human body.

What is cancer?, well I now know after watching this very insightful video. I never knew it were all down to cells that keeps either our bodies healthy or in-fact damaging our bodies.
Very well put together, I've learnt something new.